A class of compounds termed N-halamines has been shown to provide excellent antimicrobial properties, particularly for polymers and coatings containing these functional groups. These compounds possess the advantage that their precursors can be chlorinated or brominated in situ to produce biocidal activity and be rehalogenated when the oxidative halogen on the compounds has been exhausted. For example, poly-styrene derivatized with N-chlorinated or N-brominated hydantoinyl functional groups can be used to disinfect potable water (see U.S. Pat. Nos. 5,490,983, 6,548,054 B2, 7,687,072 B2) and, as a matter of fact, is currently being used for water disinfection by low-income families in developing nations such as India. The N-halamine polymer technology can further be applied to produce antimicrobial coatings on surfaces such as textiles (see for example, U.S. Pat. Nos. 6,969,769 B2, 7,335,373 B2, 5,882,357). It has recently been demonstrated that the N-chlorinated hydantoinyl siloxane polymer addressed in U.S. Pat. No. 6,969,769 B2 can also be used in detoxification of chemical agents (Salter, et al., J. Mater. Sci., 44, 2069 (2009)). Any N-halamine coating will be antimicrobial and capable of detoxification since the bound halogen is oxidative upon transfer to receptor sites. Heretofore, two limitations of N-halamine polymer coatings have been their oxidative halogen loading capacities (less than 1% by weight chlorine) and their lack of resistance to ultraviolet photodegradation. Thus, it would be desirable to create an N-halamine polymer coating which could load a higher weight percentage of halogen, so as to increase its biocidal and detoxification efficacies (lower contact times necessary for complete inactivations of pathogens and toxic chemical agents) and which could resist ultraviolet photodegradation in sunlight.
Meta-aramid (poly-m-phenylene isophthalamide), generally sold under the trade name Nomex™, is known to be an excellent fire-resistant polymer. It can be prepared by reaction of isophthaloyl chloride with m-phenylene diamine in a solvent such as tetrahydrofuran (see for example U.S. Pat. No. 3,287,324). It is used in commerce in the form of a fiber or film. It contains an acyclic amide nitrogen atom which can be halogenated by exposure to aqueous free chlorine or bromine (see chemical structure below). It has been shown that Nomex fibers achieve
chlorination with aqueous household bleach with much less decomposition than does its isomer p-aramid, trade name Kevlar, (see Sun and Sun, Ind. Eng. Chem. Res., 43, 5015 (2004)); however, a maximum concentration of only about 0.1 weight percent of oxidative chlorine (expressed as wt % Cl+) could be loaded onto the Nomex fibers in that work. This loading demonstrated antibacterial activity for the fibers, but the loading decreased substantially over time and under washing conditions, and only 0.1 wt % chlorine would not be able to provide sustained biocidal activity. Sandstrom and Sun extended the Nomex fiber work to a study of thermal and UV stability for chlorinated Nomex in firefighter uniforms (Sandstrom and Sun, RJTA, 10, 13 (2006); Sandstrom et al., Tex. Res. J., 77, 591 (2007)). Again the fibers contained very low chlorine loadings (less than 0.1 wt %), but the authors noted some UV stability over a one hour irradiation period as long as the fibers were maintained in a very dry state. Under controlled humidity tests in a weathering chamber the chlorinated fibers were not thermally or photolytically stable. It has also been shown that the loading of chlorine can be increased for fibers containing a blend of Nomex polymer and cellulose up to almost 1 wt % if Nomex and cellulose are dissolved in an ionic liquid solvent and co-extruded into fibers (see Lee et al., J. Eng. Fib. Fab., 2, 25 (2007)). Upon chlorination, the fibers became bactericidal. However, when the Nomex polymer content in the blended fibers was above 10 weight percent, the tenacities of the fibers were dramatically decreased rendering them impractical for commercial use. A similar study has been recently reported for a Nomex-coated/polyethylene terephthalate prepared by applying a dimethylacetamide solution of Nomex to PET fabric using a pad-dry-curing process (Kim et al., J. Appl. Polym. Sci., 114, 3835 (2009)). The treated Nomex/PET was antibacterial but only could load about 0.4 wt % chlorine which again would not provide sustained antimicrobial activity. The detoxification study mentioned above (Salter, et al., J. Mater. Sci., 44, 2069 (2009)) employed Nomex derivatized with the hydantoinyl siloxane of U.S. Pat. No. 6,969,769 B2. The chlorine loadings in that study were about 0.32 wt % which would be too low for sustained detoxification activity. In summary, loadings of more than 1 wt % chlorine on Nomex fibers or its co-polymer blends and sustainable UV stability under real-world conditions have not been obtained heretofore. The most probable reason for this is that the oxidative chlorine is not able to penetrate the surfaces of the fibers due to lack of porosity and low permeability of the chlorine into the polymer structure. Hence any antimicrobial or detoxification activity of the treated Nomex fibers will be short-lived due to rapid exhaustion of the bound oxidative chlorine on the surfaces of the fibers.
Thus, porous, permeable antimicrobial/detoxification particles of Nomex or its blends with other polymers such as cellulose, cellulose acetate, polyurethane, and the like, would be desirable because they should bind much more oxidative chlorine than do non-porous fibers which would enable extended antimicrobial and detoxification activity and possibly less photodegradation due to the fact that much of the halogen would be less accessible to the UV photons when buried within the pores than those halogens bound on the surface. The N-halamine polymeric biocide as an amorphous solid, which is the subject of U.S. Pat. No. 5,490,983, has been broadcast into nonwoven webs for use in personal care absorbent articles (see US Patent 2003/0144638 A1) and shown to work well for this application. The current invention which involves Nomex particles and its blends should work well in similar applications for providing antimicrobial activity as well as in numerous other applications such as water and air filters, military textiles, health care textiles, paints, and other coatings. A byproduct of antimicrobial activity is the destruction of noxious odors in personal care absorbent articles, textiles, paint coatings in medical facilities, and the like. A distinct advantage of the treated Nomex and Nomex blend particles will be its lower cost relative to other biocidal particles such as that disclosed in U.S. Pat. No. 5,490,983 and 2003/0144638 A1.
Previous work on Nomex and Nomex blends relates to the materials existing as fibers, not porous particles.